The present invention relates to a foam generating nozzle for use in fire fighting or related applications. More particularly, the invention relates to a lightweight nozzle with a central bore or passage having transverse means to create a turbulent, air entraining flow within the fluid passing through the nozzle.
Foam generating nozzles may be used in fire fighting as well as in other foam applications, such as protective coverings for plants. Foams used in fine fighting have different characteristics, depending on the type of fire. Foam used on a Class B flamable liquid fire must blanket and suffocate the first whereas when fighting a Class A fire in ordinary material foams require a quenching ability in addition.
To extinguish a Class A fire, desirably the foam generated by a nozzle should have a low expansion ratio and a long drain or dwell time to enhance the effectiveness of the foam. Foams having a low expansion will drain less rapidly from a surface which has been covered, and will adhere for a sufficient time to vertical surfaces to accomplish the necessary level of quenching or insulation. Class B fires, on the other hand, are better controlled by a medium expansion foam, with a higher density bubble matrix to suffocate the fire.
In order to develop a foam, it is necessary to achieve a turbulent interaction of the fire fighting fluid medium, usually water, a foaming agent, and a gas, usually ambient air. Many factors appear to affect the foam characteristics, including the proportions of foaming agent in water, the amount and location of air applied to the foam and, to a large measure, the structure and degree of turbulent interaction of the mixture of water and foaming agent with the air.
Previous foam generating nozzles have utilized heavy metal structures with complex apertures and passages therein.
U.S. Pat. No. 2,388,508 to Timpson discloses a nozzle with a central valve body having a pair of converging ducts or passages to cause two streams of the liquid mixture to impinge at a 60.degree. angle within a cylindrical baffle or spray straightner, before exiting into a low pressure air chamber which then feeds foam through a throat and pattern nozzles.
U.S. Pat. No. 2,513,417 to Lindsay discloses a complex nozzle with a venturi means for feeding foaming agent into the water, with a conical spreader which separates the stream of mixture in an air chamber. A further tear drop shaped baffle is required to control the velocity of the fluid to achieve a more uniform foam quality.
Both of the foregoing patents require a complex machined or cast product with specially designed fluid passages to generate an adequate foam.
The present invention, however, has achieved improved foam characteristics, both in drain time and adherence, with no increase in complexity or weight of materials. Rather, significant simplification of design has resulted in surprisingly economical manufacturing capabilities while achieving even lighter weights and improved fire fighting capabilities.
The present invention of a foam generating nozzle has a nozzle body with a longitudinal passage therethrough, an inlet at the up-stream end of the nozzle body for receiving a pressurized mixture of water and foaming agent, an outlet at the down-stream end of the nozzle body for emitting a stream of foam, a plurality of contiguous apertured plates positioned transversely across the passage between the inlet and outlet to permit passage of the mixture through the nozzle, wherein at least one plate has at least one aperture and at least one other plate has a plurality of apertures partially overlying a portion of the at least one aperture to permit passage of the mixture therethrough; and means down-stream of said plates for the induction of air into the interior of the nozzle.
It is an object of the present invention to provide a simplified nozzle structure allowing for economical and efficient manufacture, while also achieving a desirable light weight and durability.
A further object of the invention is to provide a nozzle which will generate a low to medium expansion foam with an extended drain time while retaining good range or throw characteristics.
The nature and objects of the invention and the various advantageous features are shown in the accompanying drawings illustrating preferred forms by way of example.